Process for the production of lower alkyl oligoglucosides

ABSTRACT

Light-colored lower alkyl oligoglucosides having a low polyglucose content can be obtained in short reaction times by a process in which 
     a) aqueous glucose sirup is added to a mixture of a lower alcohol and an acidic catalyst at elevated temperatures via an inline mixer, 
     b) the water present in the reaction mixture and the water released are azeotropically distilled off continuously and 
     c) after the addition of glucose sirup, the reaction mixture is subjected to heating until at least 99% of the glucose is reacted.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a process for the production of lower alkyloligoglucosides in which glucose sirup is added at elevated temperatureto a mixture of a short-chain alcohol and an acidic catalyst via aninline mixer, the water of reaction is azeotropically distilled off andthe reaction mixture is subjected to an after-reaction.

2. Statement of Related Art

Surface-active long-chain alkyl oligoglucosides have long been known asraw materials for the production of detergents. They are normallyproduced by acid-catalyzed acetalization of glucose with long-chainfatty alcohols. In the processes known as the "transacetalizationprocess" or, in special cases, as the "butanol route", the glucose isreacted with a short-chain alcohol, for example butanol, in a first stepto form the corresponding glucoside which, in a second step, issubjected to transacetalization with a fatty alcohol. Accordingly, loweralkyl oligoglucosides, such as butyl glucosides for example, areimportant intermediate products for the production of long-chain alkyloligoglucosides. In addition, they are directly used as solubilizers andemulsifiers.

European patent application EP 0 319 616 A1 describes a process for theproduction of lower alkyl oligoglycosides in which an aqueous sugarsolution is mixed with a short-chain alcohol, an acidic catalyst isadded to the homogeneous solution and the mixture is subsequentlyreacted at 60° to 200° C. and preferably at 80° to 150° C., any waterpresent being azeotropically distilled off.

International patent application WO 90/1489 describes the reaction ofglucose sirups having a DP 1 content (i.e. monomer content) of less than90% by weight with butanol. The acetalization is carried out withintensive stirring in an aqueous system at temperatures above 125° C.and under pressures of 4 to 10 bar, the reaction mixture beingpump-circulated via an inline disperser. The sirup is directlyintroduced into the reactor. After the addition, the reaction mixture issubjected to an after-reaction to ensure that the glucose is completelyreacted off.

The above-mentioned processes have disadvantages which seriously limittheir commercial value. If the glucose sirup is introduced into themixture of alcohol and acidic catalyst too quickly, it is not adequatelydispersed, even with intensive stirring. Instead, the glucose siruppasses through a tacky/viscous intermediate stage with release of water,resulting in the formation of agglomerates which are virtuallyimpossible to redisperse. These agglomerates tend to settle mainly onthe stirrer unit and cause it to stick and, in extreme cases, to clogup. In addition, another part of the non-dispersed, lumpy startingmaterial usually adheres to the heated reactor wall so that partialcarbonization can occur. The acetalization reaction between glucose andalcohol clearly cannot take place optimally where this procedure isadopted. For the most part, the reaction does not take place during theaddition, but only during the after-reaction which, for this reason, hasto be significantly prolonged.

The problem in question is normally avoided by adding the glucose sirupslowly, i.e. at such a rate that no lumps are formed, instead asingle-phase homogeneous system is present or a more or less finedispersion is formed in which the acetalization can take place withoutdifficulty. Although the after-reaction time can be shortened to aneconomically acceptable level in this way, the addition time issignificantly prolonged so that, in all, long reactor possession timesare again the outcome.

Another disadvantage of the long reaction times is that the end reactionproducts have comparatively high contents of polyglucose and otherunwanted secondary products, such as dialkyl ethers for example, and inaddition can be seriously discolored by the severe exposure to heat.

Now, the problem addressed by the present invention was to provide animproved process for the production of lower alkyl oligoglucosides whichwould be free from the disadvantages mentioned above.

DESCRIPTION OF THE INVENTION

The present invention relates to a process for the production of loweralkyl oligoglucosides which is characterized in that

a) aqueous glucose sirup is added to a mixture of a lower alcohol and anacidic catalyst at elevated temperatures via an inline mixer,

b) the water present in the reaction mixture and the water released areazeotropically distilled off continuously and

c) after the addition of glucose sirup, the reaction mixture issubjected to an after-reaction i.e. heating is continued until at least99% by weight of the glucose has reacted.

It has surprisingly been found that even highly degraded glucose sirupcan readily be dispersed in the reaction mixture if it is added via aninline mixer. In this way, the total reaction time, i.e. the sum of theaddition time and the after-reaction time, can be significantlyshortened. The lower alkyl oligoglucosides obtained are distinguishedfrom the prior-art products by a lighter color and a significantlyreduced content of secondary products.

Glucose sirup is understood to be a highly degraded aqueous starchproduct which has a solids content of 50 to 85% by weight and preferably70 to 80% by weight, based on the sirup, and a DP 1 value (i.e. amonomeric glucose content) of 90 to 100% by weight, based on the solidscontent.

Inline mixers which may be used in the process according to theinvention are high-speed rotor/stator dispersers in which the shearingelements have a suitably structured surface. Inline mixers particularlysuitable for rapid dispersion of the glucose sirup in the reactionmixture have shear rates of 10⁴ to 10⁶ s⁻¹. By suitable structuring ofthe rotor and stator rings, for example by toothing, grooving orperforation, the shear zone is made to pulse as a function of time whichintensifies the dispersing effect. Inline mixers which operate with anaverage shear pulse count per unit volume of 10⁵ to 10⁸ l⁻¹ have provedto be optimal.

The inline mixers are preferably incorporated in the liquid circuitoutside the reaction vessel. However, the mixing systems may also beoperated in a flow guide tube inside the reactor.

Lower alcohols in the context of the process according to the inventionare primary alcohols corresponding to formula (I)

    R.sup.1 -OH                                                (I)

in which

R¹ is a linear or branched alkyl radical containing 3 to 8 carbon atoms.Typical examples are n-propanol, isopropyl alcohol, i-butanol, sec.butanol, tert. butanol, pentanol, hexanol, heptanol, n-octanol and2-ethyl hexanol. n-Butanol is preferably used.

The acetalization is carried out in the presence of acidic catalysts.Typical examples are methanesulfonic acid, butanesulfonic acid andsulfosuccinic acid. p-Toluenesulfonic acid is preferably used.

To displace the acetalization equilibrium onto the glucoside side, it isadvisable initially to introduce the lower alcohol in a considerableexcess. Typically, the glucose and lower alcohol may be used in a molarratio of 1:3 to 1:10 and are preferably used in a molar ratio of 1:6 to1:8.

The acidic catalyst may be used in a quantity of 3·10⁻³ to 2·10⁻² moland is preferably used in a quantity of 5·10⁻³ to 1·10⁻² mol per molglucose.

The alcoholysis of the glucose is preferably a butanolysis. It isadvisable in this regard initially to prepare a solution of the acidiccatalyst in the excess lower alcohol, to heat the mixture to thereaction temperature of 100° to 115° C. and preferably 108° to 113° C.and continuously to introduce the glucose sirup over a period of 0.1 to3 and preferably 1 to 2 h at such a rate that a fine-particle dispersionis formed. "Fine-particle" in the present context means that thedispersion is free from clearly visible, tacky agglomerates.

In one embodiment of the process according to the invention, the mixtureof glucose sirup, lower alcohol and catalyst is circulated through afalling-film evaporator. The large material transfer surface, theminimal film thickness and the high throughflow rate provide for theparticularly gentle transfer of heat and for the highly efficientevaporation of water from the reaction mixture which is reflected in ahigh color quality of the end reaction products.

To establish the equilibrium, both the water from the glucose sirup andthe water of reaction have to be removed as quickly and as completely aspossible from the reaction mixture. This is preferably done by means ofa standard distillation column through which an azeotropic mixture ofwater and lower alcohol can be removed. Where butanol is used as thelower alcohol, an azeotrope boiling at around 93° C. is formed and canbe distilled off particularly easily.

The alcohol/water mixture removed via the column can be separated in aseparation vessel into an upper high-alcohol phase, which is returned tothe column, and a lower low-alcohol phase which is separately worked up.This ensures that the process is attended by a minimal loss of loweralcohol.

Addition of the glucose sirup is followed by an after-reaction for about0.1 to 2 h and preferably for 0.5 to 1.5 h at a temperature of 100° to115° C., during which it is ensured that all the glucose, i.e. at least99% by weight, based on the quantity used, has reacted off. The end ofthe reaction is also signaled by an increase in temperature in thedistillation column when only pure lower alcohol rather than thewater/alcohol azeotrope is evaporated.

INDUSTRIAL APPLICATIONS

The lower alkyl oligoglucosides produced by the process according to theinvention are obtained in short reaction times, have a polyglucosecontent of less than 2% by weight and preferably less than 1% by weight,based on the solids content of the product, and are distinguished bygood color quality.

They are suitable, for example, as intermediate products for theproduction of relatively long-chain alkyl oligoglucosides for laundrydetergents, dishwashing detergents and cleaning products and forhair-care and personal hygiene preparations in which they may be presentin quantities of 0.1 to 50% by weight and preferably in quantities of 1to 25% by weight, based on the particular product.

The following Examples are intended to illustrate the invention withoutlimiting it in any way.

EXAMPLES Example 1

2,000 g (27 mol) n-butanol and 12.7 g p-toluenesulfonic acid wereintroduced into a 4-liter stirred reactor and heated to 107° C. under apressure of 750 mbar. The reaction mixture was pump-circulated through amixing chamber equipped with a mixer of the Ultra-Turrax® type arrangedoutside the reactor. 1,160 g glucose sirup (solids content 70% byweight, glucose content 96% by weight, based on solids), correspondingto 4.5 mol glucose, were introduced into the liquid circuit via themixing chamber of the Ultra-Turrax® over a period of 2 h, a finedispersion of the glucose in the butanol being formed.

The water of reaction and water which had been introduced with theglucose sirup were distilled off in the form of a butanol/waterazeotrope.

The condensate was separated in a separator and the butanol-rich phasewas returned to the reactor.

After the addition, the reaction mixture was subjected to anafter-reaction for 1 h at 107° C.

The test results are set out in Table 1.

Example 2

870 kg butanol and 4.3 kg p-toluenesulfonic acid were introduced into a3.2 m^(s) reactor and heated to 110° C. under a pressure of 950 mbar. Aliquid circuit was built up through a pump, an inline mixer (Cavitron®1039, rotational speed 3100 r.p.m.) and a falling-film evaporator. 470kg glucose sirup (solids content 70% by weight, glucose content 96% byweight, based on the solids content) were introduced into the inlinemixer over a period of 3 h.

The water of reaction and water which had been introduced with theglucose sirup were distilled off in the form of a butanol/waterazeotrope.

The condensate was separated in a separator and the butanol-rich phasewas returned to the reactor.

After the addition, the reaction mixture was subjected to anafter-reaction for 1 h at 110° C. The test results are set out in Table1.

Comparison Example C1:

The procedure was as in Example 1, except that the glucose sirup wasintroduced into the reactor directly, rather than through theUltra-Turrax® over a period of 2h Instead of a fine dispersion, it wasfound that the glucose sirup had hardly dispersed in the reactionmixture, but instead had settled on the wall of the reactor andparticularly on the stirrer. The after-reaction time was increased to2.5 h. Due to partial carbonization of the glucose sirup on the reactorwall, there were black solid particles in the product. The results areset out in Table 1.

Comparison Example C2:

The procedure was as in Example 2, except that the glucose sirup wasintroduced into the reactor directly, rather than through the inlinemixer, over a period of 2 h. Once again, no fine dispersion wasobtained, instead the sirup had settled on the stirrer and the reactorwall. The results are set out in Table 1.

                  TABLE 1                                                         ______________________________________                                        Test results, percentages as % by weight                                            t(A)   t(ARc)                     c(PG)                                 Ex.   h      h       Dispersion                                                                             Product   %                                     ______________________________________                                        1     2      2       Fine-particle                                                                          Light-colored,                                                                          <1                                                                  clear                                           2     2      1       Fine-particle                                                                          Light-colored,                                                                          <1                                                                  clear                                           C1    2      2.5     Lumpy    Discolored,                                                                             2.1                                                                 carbonization                                   C2    2      3       Lumpy    Discolored,                                                                             2.5                                                                 carbonization                                   ______________________________________                                         Legend:                                                                       t(A) = Addition time                                                          t(ARc) = Afterreaction time                                                   c(PG) = Polyglucose content                                              

What is claimed is:
 1. A process for producing a lower alkyloligoglucoside comprising the steps of:(1) adding an aqueous glucosesirup to a heated mixture of a lower alcohol and an acidic catalyst inan inline mixer; (2) removing the water of solution and the water ofreaction from the resulting mixture by azeotropic distillation with saidlower alcohol; and (3) heating the mixture following step (2) until atleast 99% of the glucose is reacted.
 2. The process of claim 1 whereinthe solids content of said glucose sirup is from about 70 to about 80%by weight.
 3. The process of claim 1 wherein the inline mixer is a highspeed rotor/stator disperser.
 4. The process of claim 1 wherein theprocess includes the use of a reaction vessel.
 5. The process of claim 4wherein the inline mixer is positioned outside the reaction vessel. 6.The process of claim 4 wherein the inline mixer is in a flow guide tubeinside the reaction vessel.
 7. The process of claim 1 wherein the loweralcohol is butanol.
 8. The process of claim 1 wherein the shear rate insaid inline mixer is from about 10⁴ to about 10⁶ s⁻¹ ; the lower alcoholis a compound of the formula R¹ --OH wherein R¹ is a linear or branchedalkyl radical having from 3 to 8 carbon atoms; and the molar ratio ofglucose to lower alcohol is from about 1:3 to about 1:10.
 9. The processof claim 8 wherein the lower alcohol is butanol.
 10. The process ofclaim 1 wherein the solids content of said glucose sirup is from about50% to about 85% by weight.
 11. The process of claim 1 wherein themonomeric glucose content of said glucose sirup is from about 90% toabout 100% by weight of the solids content.
 12. The process of claim 1wherein the shear rate in said in-line mixer is from about 10⁴ to about10⁶ s⁻¹.
 13. The process of claim 1 wherein the average shear pulsecount per unit volume in said in-line mixer is from about 10⁵ to about10⁸ s⁻¹.
 14. The process of claim 1 wherein said lower alcohol is acompound of the formula I

    R.sup.1 --OH                                               (I)

wherein R¹ is a linear or branched alkyl radical having from 3 to 8carbon atoms.
 15. The process of claim 1 wherein said acid catalyst isp-toluenesulfonic acid, methanesulfonic acid, butanesulfonic acid, orsulfosuccinic acid.
 16. The process of claim 1 wherein the molar ratioof glucose to lower alcohol is from about 1:3 to about 1:10.
 17. Theprocess of claim 16 wherein said molar ratio is from about 1:6 to about1:8.
 18. The process of claim 1 wherein the molar ratio of acid catalystto glucose is from about 3×10⁻³ :1 to about 2×10⁻² :1.
 19. The processof claim 1 wherein in step (1) said mixture is comprised of a fineparticle dispersion formed by adding said glucose to a solution of saidacid catalyst in said lower alcohol over a period of from about 0.1hours to about 3 hours at a rate sufficient to form fine particles. 20.The process of claim 1 wherein step (3) is carried out at a temperatureof from about 100° C. to about 115° C.